Indicating or control apparatus responsive to temperature variations



March 2, 1954 F F. RAMSAY 2,670,989

R. INDICATING OR CONTROL APPARATUS RESPONSIVE TO TEMPERATURE VARIATIONSFiled April 11, 1949 F/GJ.

' v /2 J l/ Inventor Attorneys Patented Mar. 2, 1954 INDICATING ORCONTROL APPARATUS RE- SPONSIVE TO TEMPERATURE VARIATIONS Frank RaymondFaber Ramsay, East Sheen, London, England, assignor to D. Napier & SonLimited, London, England, a company of Great Britain Application April11, 1949,'Serial No. 86,653

Claims priority, application Great Britain April 22, 1948 2 Claims. (01.297-) This invention relates to indicating and control apparatusresponsive to temperature variations, and has for its object to providea form of apparatus which will be particularly suitable for indicatingor efiecting control in accordance with variations in temperature in ahigh temperature zone within a predetermined high temperature range,will enable a high degree of sensitivity and/or an adequate controllingforce to be obtained for temperature variations within that range andwill provide for quick response to such variations, while having asubstantial margin of safety from damage caused by accidentaloverheating.

Various forms of temperature responsive indicating and control apparatushave been proposed comprising a fluid-filled chamber, hereinafterreferred to for convenience as a bulb, connected by a tube to a devicewhich moves in response to changes in pressure Within; the apparatuswith resultant changes of volume, the most common device of thischaracter being the, Bourdon tube, which either actuates an indicatingneedle or the like or exercises control over appropriate mechanism. Inone such'apparatus as hitherto proposed the bulb and pressure responsivedevice have been filled with liquid and the thermal expansion andcontraction of the liquid under the influence of variations intemperature have caused the movement of the pressure responsive deviceso as to accommodate the changes in volume of the liquid, while, in analternative arrangement, the bulb, tubeand pressure responsive devicewere partly filled with liquid and partly with the vapour of the liquid.and the movement of the pressure responsive device was produced byvariations in the vapour pressure of the liquid with temperaturevariations; It will be seen that, in the former proposal the exactpressure exerted on the liquid by the pressure responsive device atdifferent points in the range of movement was immaterial, the liquidbeing substantially incompressible, while in the latter case, to giveaccurate results, its pressure response curve had to be accuratelydetermined.

With the devices operating by thermal expansion the expansion of theliquid for any given temperature rise is comparatively small and if acomparatively large movement of the indicating or control mechanism isrequired, either movement multiplying mechanism must be employed, with acorresponding reduction in the force which can be applied thereby, or alarge volume of liquid must beprovided in the bulb, which not only makesthe response-to temperature variations sluggish but may be inconvenientor impossible to provide for reasons of space, in many applications.Moreover the thermal expansion devices are influenced by the thermalexpansion of the various parts of the apparatus containing the liquidthus entailing errors or necessitating mechanism for compensating forvariations in atmospheric or other temperatures to which the parts ofthe apparatus are subject outside the zone in which the bulb lies.

With devices operating by variation in vapour pressure and where acomparatively large movement or force is required from the pressureresponsive device for comparatively small variations in temperature, itis necessary to use a liquid which over the predetermined rangeior whichcontrol or indication is required (hereinafter called the predeterminedtemperature range) is in the higher temperature part of its usable rangeof vapour pressures. This is because towards the high temperature end ofthe usable range of vapour pressures 'there is a comparatively largepressure variation for a given temperature variation, whereas thepressure variation for a given temperature variation progressivelydecreases towards the lower end of such range.

Since, however, the device must also allow for the temperature to dropdown to atmospheric temperature, for example when the apparatus withwhich it is used is out of operation, if the predetermined temperaturerange is high, the pressure responsive device has to allow for expansionand contraction over the whole range' from atmospheric temperature up tothe highest temperature within the predetermined temperature range. Itis moreover an essential of devices of the kind in question that thereis always some liquid present in the bulb and therefore subject to thecontrolling temperature, but if the predetermined temperature range ishigh the expansion of the pressure responsive device during the rise intemperature to reach that range will be such as to take all theliquid'out of the bulb before the predetermined temperature range isreached. To avoid this either the bulb must be made comparatively large,which makes the apparatus sluggish, or the pressure responsive devicemust be such that it expands little for large variations in pressurewhich means'that the device will be insensitive and provide littlemovement for variations in temperature within the predetermined range.

Further, since for apparatus designed to operate at hightemperaturesthe' bulb has to withstand high pressures, it is desirableto keep the bulb as small as possible both to enable it more readily tobe made ofwadequate strength and to facilitate its accommodation withinthe high temperature zone.

The size of the bulb limits the maximum internal pressure and hence thetemperature which such apparatus can measure with accuracy, since theapparatus will only work. accurately if the walls of the bulb do notyield appreciably due. to the internal pressure. It has hitherto beennecessary in thermometers'oi the liquid filled and vapour pressure typesto provide a bulb of comparatively large size in order to ensure thatthere is always some liquid in the bulb, and this has limited themaximum permissible internal pressure and hence has restricted maximumworking temperature, in the case where the liquid is mercury, to about650 C.

p Th object of the present invention is to provide apparatus forindicating or control in accordance with the temperature in a hightemperature zone within a predeterminedhigh temperature range which willbe less subject to "the difiiculties and limitations-referred to aboveas present in the known types of apparatus and will thus tend toprovidean apparatus particularly well suited to its purpose.

The invention is particularly but not exclusively applicable toapparatus in which indica- 'tion or control is desired in accordancewith temperatures such as those which prevail, for ex- "ample, inthe'blade chamber of a combustion turbine.

Apparatus according tothepresent invention for indicating or controlin'accordance with the temperature in a high temperatur zone within apredetermined high temperature range com- :prises aclosed chamberhavingone part which -is adapted to lie in the high temperature zone:andan'other part which is adapted to lie outside this zone, the latterpart including a .device which moves inresponse to changes in pressurwithin 1the.chamber with resultant changesin the vol- -umeiof thechamber, the chamber at tempera- Eturessbelow thesaid'ihigh' temperaturerange being Wholly filled with liquid under a pressure which; exceedsthevapour pressure of the liquid, ;while:at temperatures within the saidrange the :vapour pressure of theliquid determines the :pressure in'ithechamber and the liquid in the TfiISt -mentined .part of the chamber atleast partly'vaporises, whereby the movement of the ipressure responsivedevice below the. said high ftemperature :range' is :in accordance with.the thermal expansion of .the liquid, while its move- :mentwithinthe-said range iscin accordance with :the variations in the vapourpressure of the .1iquid.

.Ihusover the temperature range below the predetermined high temperaturerange the 'pressure-inthe chamber exceedsthe vapour pressure tof theliquid and th chamber thusremains filled with liquid whereas over thepredeterminedhigh temperature-range the-pressure responsive device has.a substantial range .of movement in whichitsposition is. determined andmaintained by. vapour pressure.

xfIfhe .bu1b,r-that is "the part of the apparatus adaptedtolielinthehigh temperature zone, may consistof asmall'bore tube closed at one endoraplurality of small bore tubes in parallel, and the pressureresponsive device'mayconsist of a -Bourdontube, these parts beingconnected 'togetherby a suitable length of capillary tubing 4 and thewhole constituting th said closed chamber. The volume of the bulb shouldbe approxi- .mately.equal,to..the volumerof liquid required to expandthe Bourdon tubeqirom the lower to the upper end of the said hightemperature range,

so that the bulb is full of liquid at the lower end of the range butcontains only vapour at the upper end of the range.

. the said. high temperature range so that the wholeiofithisrange iswithin the part of the temperature-vapourpressure curve of the liquid inwhich comparatively small variations of temperature producecomparatively large variations 1 .in vapour: pressure.

If the movement due to variations in pressure within .the said hightemperature range is to be large the characteristicrof the pressureresponsive device must normally be such that the pressuretherein'wilromy rise comparatively little due to the thermal expansionof the liquid below the-said high" temperature range. This means that apressure-responsive device must be used which has comparatively largemovement for small variations in pressurabut it must befilled withliquid at a sufiicient initial pressure to prevent the formation 'ofvapour until the lower end of the saidhigh temperature range is reached.In practice this will generally. mean that the apparatus is 'filledatallow-temperature, e. g. room temperatureor thereabouts, with liquid ata'pressure approaching the vapourpressure of the liquid at the lower endof the said high temperature range. "Theliquid, used may c0nveniently bemercury.

' The invention may be-carried into practice in various ways-but oneparticular'construction of apparatus comprisingan override fuel controlfor a combustion turbinein-anaircraft propulsion plant, and which worksin .dependence'on the temperature inLthe blade chamber, will bedescribed byway of example with reference to the accompanying drawingsin which,

Figure l is a sectional elevation of. the apparatus, and

Figure 2 isa graphillustrating the relationshipsbetween the temperatureand the pressure andvolume of the :liquidorliquid and vapour :thebl'adeichamber oiltheturbinein such a man- :nerithat it is iexposedto'the hot gases flowing to theturbine.

Secured .=to the" bulb .and communicating with itsinterior isa-capillaryttube; l2 which leads to a housing i3 which may be mounted inany convenientpositionbn the aircraft. The other end of the capillarytube communicates with the interiorof a Bourdon' tube l4 situated withinthe housing I 3 One end of the Bourdon tube I4 bears against astationaryabutment-IS which is provided with means whereby" it can beadjusted, while the other end bears against a" lever 56 which is pivotedin'the'housing'by its upper end' i l.

Aspring I-8'bea'rs'against'the lever I [i in opposition to theforceexerted by'the Bourdon tubelever will depend upon the initialloading and characteristic of the spring, and also upon the forceexerted by the Bourdon tube M. The outer end of the spring 18 bearsagainst an adjustable abutment 20 by which its initial loading can beadjusted.

The force exerted by the Bourdon tube I4 can be used to actuate a greatvariety of control or indicating mechanisms or devices, but in thepresent arrangement, which is given purely by way of example, itcontrols the amount of fuel which can be bled off through an orifice 2|which in turn controls the stroke of a variable stroke fuel pump and inthis manner regulates the amount of fuel supplied to the burners in thecombustion chambers of the turbine.

The bulb [0, the capillary tube l2 and the Bourdon tube 14 are filledwith mercury under v the operating range some of the mercury containedin its is vaporized so that the pressure in the bulb ID, the capillarytube l2 and the Bourdon tube 14 is equal to the vapour pressure ofmercury atthis temperature. The Bourdon tube [4 will exert a pressure onthe lever IS in opposition to the spring 18 proportional to the pressureinside it, and therefore proportional to the temperature of the bulb H1.The clearance between the lower end IQ of thelever l6 and the orifice 2|will therefore depend on the pressure in the Bourdon tube [4 and henceon the tem perature of the bulb I0. Within the operating range thehigher the temperature of the bulb H) the greater will be the pressurein the Bourdon tube l4, and hence the greater the clearance between thelower end IQ of the lever 16 and the orifice 2|. This will bring about areduction in the stroke of the fuel pump and hence there will be areduction in the amount of fuel supplied to the burners. The apparatustherefore provides an automatic temperature override control and can beadjusted so that it tends to maintain the temperature of the gasesentering the turbine at a substantially constant value within the saidrange.

The internal diameter of the bulb l ispreferably small so that whenmercury vapour forms .therein during operation within the 'hightemperature range the surface tension of the mercury will cause thevapour to be formed and maintained as a single stable bubblesubstantially filling an appropriate length of the bulb, that is to saythe surface of the liquid mercury at the end or ends of the bubble willextend across the bore of the bulb as does the liquid in a normal liquidthermometer. In this way unsteadiness in the operation of theapparatus-due to turbulence of the liquid and vapour in the tube duringchanges in temperature tends to be avoided.

For the operating conditions mentioned above suitable dimensions for thebore of the bulb I!) have been found to be 0.705 to 0.708 long by 0.050"in diameter. One way in which these dimensions may be determined will bedescribed below. r

The dimensions of the bulb in relation to those 6. of the hot zoneshould in any case be such that the whole of the bulb is in the hot zoneso that the temperature of the whole bulb is substantially uniform. Inpractice this will usually entail a short length of the capillary tubeadjacent to the bulb also lying in the hot zone as shown in the drawing.

The operation of the apparatus may be analysed as follows: 7

The operation depends upon the fact that the thermal expansion of aliquid follows an approximately straight line law while the vapourpressure of the liquid is governed by a higher law. The accompanyinggraph (Figure 2) illustrates the functioning of the apparatus shown inFigure 1 and for convenience in the description the following symbolswill be used:

To=temperature at which the bulb is initially filled. T1=temperature atthe start of the control range. Tz te'mperature at the end of thecontrol range. t=ambient temperature of the capillary tube and theBourdon tube. Pu=filling pressure (static). P =vapour pressure at T1.P2=vapour pressure at T2. Vo=volume of the bulb, after filling, at T0.V1=volume expansion of the Bourdon tube from T0 to T1. 7 a 7 V2=volumeexpansion of the Bourdon tube from T0 to T2. i=coefficient of cubicalexpansion of mercury. fl=coefiicient of cubical expansion of the bulb.

=ratio of pressure increase to volumetric expan sion of Bourdon tube.

Referring to Figure 2, the volume expansion of the Bourdon tube is shownon the left hand scale. Changes in the volume expansion are proportionalto changes .in the pressure P within the apparatus, which is shown inthe right hand scale. The temperature-vapour pressure curve for anygiven liquid, in this case mercury, is invariable and is shown at A. Fora given temperature control range T1 to T2 thecorresponding pressurerange P1 to P2 is therefore known. The corresponding volumetricexpansion of the Bourdon tube, V2V1, can then be marked off on the lefthand. scale.

The volume of the bulb at T1 is Now at T1 the bulb is still full ofliquid mercury, the volume of which must also be At the temperature Tothe volume of mercury present in the bulb was V0, which at the temperature T1 would occupy the volume Vo[1+a(T1-T0)] Thusa' quantity ofmercurymust have been ex'pelled from the bulb'in rising from To to'T1,this quantity having at T1 the volume:

Voll+o.(T1-To)l-+Vo[l+,8(T1-Tu)l u I. =V0(a,8)(T1-T0) Now supposing thisexpelled ume a: a'tTo.

Then at t it would have the volume I. .I ..."..-f which by definition isthe volume V1.

1+a(t-T mercury has a vol- Thus,

aevosma zAt mi zthe expelled: mercury -.\vou1d ahave :the volumezv'l'zl+eil'i-iTo)..l.. But this volume has already beenizfound' *to;:be' ;VOQa fl)1(fl1:-To-). Therefore.

'18]:1+al(Tl To){]j V(a-*B)-(T1T0) and substituting for a: theexpressiontobtained above,

At .T2 the bulb no longencontainsmercurv, and if the vapour-inthelbulbbe ne lected anamount ofmercury with. a-volume V -at Ioihas beenexpelledfrom thebulblinto the Bourdon tube and. here hasacquired thetemperature t. The volume f this ury at .theitemperaturesequ ls thevolumetric expansion V2 of the Bourdon tube from Toto T2. 'Inotherwords,

*Since :a change in pressure-is pmportional 0 the volumetric expansionofzthe :Bourdontube,

characteristic. of the tube mustbe measured, and it isthen possible tocal'culatevo and Po 'from'the above equations 1 01" any desiredtemperature range;

AltematiVeIy, starting with aibulb of a given volume,thecharacteristicsofthe Bourdon tube and theestatic pressure aand v forthe desired temperature range can be worked out.

A lower :limit torthezvolume \Pov of the .bulb M is approached when thevolume-of liquid in the capillary tube !2 begins to be appreciable incomparison with that or thebulb tflg since the ambient temperaturearound the hot end of the capillary tube changes considerably inpractice-and this would cause an excessive 'shift of the temperaturelimits 'inzthe control rangeif, the volume ofliquid in :the capillarywere comparable with that of the bulb.

It will be ahharentthat-with apparatus according tothepresent invention,since the formation of vapour within the bulb only begins when thetemperature reaches thel lower end T1 of the predetermined hightemperature range within which the control-is'mequired, the bulb isfilled with l quid at the temperature .121 with the result that for agiven size of bulb the arrangement provides for 'the 'maximumdisplacement of liquid from the bulb under rises in vapour pressurebefore the bulb becomes-em ty and the qu therefore,.;uo s lencer subictit the temperature intheihi hltemperaturezon Thus, fora enpredetermined high, temperature range T2'I' 1 and a given requiredrelationship between temperature:changes and the movement of or forceexerted by the pressure responsive device, the volume 1V0 of :t-he bulb.can 'besmall since the operationgot-ethe. apparatus as a vapour pressureresponsiveapparatusis limited solely to the predetermined rhightemperature range. Conversely for-a ,given size pi bulb the maximummovement of orforcerapplied by th pressure responsive device can beobtained overthe-predetermined high temperature range within whichindication or control is-ldesired. Thus theapparatus tends to have ahigh degree of sensitivity and quick respouse; and; to be capableiofexerting a comparatively largeacontrolling force over the requiredhigh-temperature-range since its efiective operation is limited to thatrange. Moreover, apart from a small degree- ,of bodily shifting of therange :along the, temperature-vapour pressure curve, theapparatusiscompletelyunafiected by temperatureorsother-conditions;andalwaysoperates precisely in accordance with thetemperaturein thehigh temperature zone, in spiteof-such bodily shifting,so that no compensation has to be provided for.externaliniiuenoes.Agaimsince the apparatus uses .thapart of the temperaturevapour pressurecurve of the liquid over which comparatively small variations intemperature produce comparatively large variations .in vapour pressure,a very closecontrolin accordance w th the temperature conditions in thehigh temperaturezone can-be achieved.

Furthermore, if the bulb tis accidentally .overheated beyond the. upperlimit or the high temperature. rangejfor which the apparatus is adaptedto function byrmovementof theBourdon tube or other pressure responsivewdevicetin accordance with variations in the vapour pressure of the qu ek dama e to he app a us by reason of the increasein pressure therebycaused is small because the increase inpressure of the vapour in thestate of a dry gas is small in comparison with the increase in thevapour pressure of a boiling liquid upon raising its temperature.

It will-"be appreciated, that. many modifications may be madeftotheconstruction specifically described. For-instance, instead of havingonly a single elongated bore the bulb may be made shorter and of greatertotal cross-sectional area, but divided into aplurality ofvchambers ofsmall cross-section, e. g. resembling a honey comb such thatthe-liquidisself-supporting in the bulb or each of the small chambersbyreason of its surface tension.

What I claim as my invention and desire to secure-by Letters Patent is:

l. Apparatus responsive to the-temperature in a high temperaturezone-within a predetermined high temperature range, which consists of aclosed chamber comprising a small bore tube closed atone end'and adaptedto lie in said high temperature zone and a Bourdon tube connected tosaid small bore tube by a length of capillary tubing, said Bourdon tubeand at least part of the capillary tubing being'adaptedto lie outsidesaidhigh temperature zone-the volume of said smallbore tube beingapproximately equal to the volume expansion of said "Bourd'on tubefrom the lowerto the upper end-of said high temperature range, andmercury within said chamber under a pressur exceeds zthe vapour-pressureof mercury at temperatures below said high temperature range, saidchamber being completely liquid filled at such lower temperatures, whileat temperatures Within the said high temperature range the mercury is atleast partly vaporised in the small bore tube so that its vapourpressure determines th pressure in the chamber, said small bore tubebeing completely filled with vapour at the upper end of said hightemperature range, whereby the movement of the Bourdon tube below saidhigh temperature range is in accordance with the thermal expansion ofliquid mercury while its movement within said high temperature range isin accordance with the variations of the vapour pressure of mercury andabove said high temperature range its movement is in accordance with thethermal expansion of mercury vapour.

2. Apparatus as claimed in claim 1 in which said high tempearture rangeincludes temperatures substantially in excess of 650 C.

FRANK RAYMOND FABER RAMSAY.

10 References Cited in the file of this patent UNITED STATES PATENTSOTHER REFERENCES Rhodes, pages tie-68 of Industrial Instruments forMeasurement and Control, by Thomas J. Rhodes, published 941 by theMcGraw Hill Book Company.

